Radio receiving system



Feb. 27, 1934. .Gl P, ADlR RADIO RECEIVING sYsTEu Filed Sept. 8, 1931 4Sheets-Sheet 1 .H IIMU um.

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ATTORNEY Feb. 27, 1934. G. P. ADAIR RADIO RECEIVING SYSTEM 4Sheets-Sheet 2 Filed Sept. 8. 193;

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, m ILMUHH ATTORNEY Feb. 27, 1934. G. P. ADAIR RADIO RECEIVING SYSTEM 4Sheets-Sheet 3 Filed sept. 8, 1931 l NVENTOR.

'Im N K @uw/7 k) I ATTORNEY um MNR w w qb m WhHMH Feb. 27, 1934. G. P.ADAIR RADIO RECEIVING SYSTEM Filed Sept. 8, 1931 4 Sheets-Sheet 4INVENToR.

RNEYv v 3 Patented Feb. 27, 1934 -PArsN'n .ori-ica RADIO RECEIVINGSYSTEM George P. Adair, San' Antonio, Tex. I Application september s,1931. serial No. 561.158

17 Claims.

My invention relates broadly to radio receiving systems and moreparticularly to a novel circuit arrangement for radio broadcastreceivers.

One of the objects oi my invention is to provide a circuit arrangementfor a radio broadcast receiver having means for controlling theoperation of the circuits of the receiving system according to thecharacter of the received signals.

Another object of my invention is to provide 1-0 a circuit arrangementfor a radio broadcast receiver having means for controlling the responseoi the receiver to musical programs and short announcements whileeliminating programs constituted by extended speeches or advertisingtalks.

Still another object of my invention is to provide a circuit arrangementfor a radio receiving system having means for discriminating betweenprograms of extended speech and advertising,

and programs of musical selections or vocal renditions in order to meetthe preference oi many listeners who do not desire to listen to programsof continuous speech.

A further object of my invention is to provide a control circuit foroperation with a radio broad- 5 cast receiver for discriminating againstprograms of musical variety and programs constituted by extended speechand advertising talks with means .for automatically tuning the receivingapparatus to programs of music while rejecting programs oi 0 speech andadvertising talks.

A still further object of my invention is to provide a circuitarrangement tor a radio broadcast receiver automatically operative uponreceipt of speech programs for disconnecting the radio broadcastreceiver and connecting an automatic phonograph or other automatic soundreproducing system to the audio frequency amplification circuits of thereceiver to insure a continuous musical program without interruption byextended advertising talk and speech.

Another object of my inventionis to provide an automatic control circuitoperative to discriminate .between voice programs and musical programsreceived over a radio receiving circuit with switching means forautomatically tuning the receiving apparatus either toa signalingchannel on which music is being received or to a control circuitextending from an automatic phonograph or other form of automaticprogram storing apparatus, such as the telegraphone, silent motionpicture, or motion picture with sound.

Other and further objects of my invention reside in the radio receivingsystem and associated ycontrol circuits set forth in the specificationhere- RE'iS'SULi inai'ter following by reference to the accompanyingdrawings, in which:

Fig. i diagrammatically illustrates a circuit arrangement ior a radiobroadcast receiver embodying .the principles of my invention; Fig. 2shows a circuit arrangement for a receiving apparatus embodying myinvention in which automatic switching means are provided for switchingthe audio frequency amplification system or the receiving apparatus to acontrol circuit leading from an automatic phonograph or other automaticprogram storing device while the radio receiving apparatus isdisconnected during the transmission of speech programs; Fig. 3illustrates a modiiled circuit arrangement embodying my invention inwhich means for automatically selecting another station ltransmitting amusical program is provided when an extended voice program isencountered on one signaling channel; and Fig. 4 shows a number ottypical sound wave traces which explain the operation oi the radioreceiving apparatus ci my invention.

In the receiving system of my invention I employ a system of vtunedcircuit for the reception ci' signaling energy in connection with anamplilisation and sound reproduction system. Supplementing the detectionand amplifier circuits I provide an auxiliary control circuit whichdiscriminates in its operation between signaling energy resulting frommusical programs and signaling energy resulting from voice programs. Inthe auxiliary control circuit of my invention l.' provide a relayarrangement by which the bias potential upon a control grid of a controltube may be governed in accordance with the character of the incomingsignaling energy. The output circuit of the controll tube operates arelay system which may perform many functions such as the opening of thesound reproducer circuit, the opening of the radio receiving circuit tothe main'detector tube of the receiver, the switching of an automaticphonograph or other automatic program storing device in the inputcircuit oi the audio frequency system oi the ampliiication receiver orthe actuation of a selector switch for tuning the receiving apparatus tosome other signaling channel on which musical programs may be received.f

The characteristics of the speaking voice are such that there arenumerous and denite pauses between syllables and words as well as thelonger pauses between phrases and sentences while in vocal andinstrumental music (except in very exceptional cases) there areiew'denite pauses. Ii the electric waves corresponding to the abovementioned signals are rectified it is found that in the case of speech apulsating current is obtained while in the case of music it is a directcurrent of moderately varying amplitude.

'Ihe character of the audiofrequency signals to which the control systemresponds is further dierentiated by an arrangement of selective ilter sothat the average frequency of speech which is lower than the averagefrequency of music produces different conditions in the operation of therelay system which correspondingly controls the switching mechanism.

Referring to the drawings in detail, the system includes a receivingcircuit having an antenna ground connection shown at 1-2 in Fig. 1. Theantenna ground connects to an input circuit including primary winding 3of the coupling transformer 4. Secondary winding 5 of couplingtransformer 4 is tuned by variable condenser 6. 'lire tuned circuitconnects to the input system of a radio frequency amplifier includingelectron tubes 7, 8 and 9. The detector tube 10 connects to theoutputcircuit of the radio frequency amplier system. The tuning elements6, 11, 12 and 13 for the radio frequency stages and thev detector stageof the receiving system are simultaneously controlled as indicatedthrough dotted line 14. The output circuit of the detector tube 10connects to the audiofrequency amplifier system constituted by electrontubes 15 and 16 connected in parallel for obtaining greater poweroutput. The output circuit of the audiofrequency ampliiler stages 15--16include the audiofrequency transformer 17, the primary winding of whichis indicated at 18 connected to the output circuit of tubes 15 and 16through the coupling condenser 57 and the secondary winding of which isindicated at 19 connected to the sound reproducer designated at 20.Themovable coil 21 of the electro-dynamic speaker system constitutingthe loud speaker 20 is connected in series with contact 22 of a relaysystem indicated at 23 and which will be described hereinafter. Thefield winding of the electro-magnetic sound reproducer 20 is shown at 24suitably energized from the power supply system formed by the rectifiercircuit 25.

A path or connection is taken from the output circuit of the detectortube 10 as shown at 26. This connection is not necessarily made at thispoint but may be made prior tc the detector stage, as shown by Figs. 2and 3, or may be made after the detector stage as conditions warrant.This path or connection leads to an auxiliary control tube 27, the inputcircuit of which is provided with a selective filter coupling deviceincluding capacity elements 28 and 30 and inductive element 29. Acoupling resistor 31 is provided for completing the input circuit to theauxiliary tube 27. If it is desired to make the selective filter moreeffective an inductive element similar to 29 may be substituted forresistor 31. Additional filter stages may be added if conditions make itdesirable. The grid 27e of control tube 27 is normally biased to anegative potential of such value that the tube is operatingon or belowthe lower knee of the characteristic grid voltageplate current curve.This negative potential is provided through resistor 31connected to thevground which is maintained at a negative potential withrespect tocathode 27a by means of the voltage drop .due to a current flow throughresistor 48, thel circuit of which is completed through resistor50 andconductor 34 to the power supply which will be hereinafterdescrlbed.-C8- pacitor 51 serves as a by-pass or smoothing condenser.

The output of the control tube 27 leads from the anode 27h to thesolenoid winding 32 forming part of a'relay. Solenoid 32 has its circuitcompleted with a resistance element 33 which leads through conductor 34to the power supply circuit. Suitable by-pass or smoothing condensers 35and 36 are connected to given points of the output circuit and ground asshown.

The relay 32 controls the movement of armature tongue 37 which shiftswith respect to contacts 38 and 39. A vacuum tube relay has beenindicated at L11 having an input circuit emending through the conductorindicated at 42 which connects to tongue 37 of the relay. Movement ofthe armature or tongue 37 against contact 39 places an increasingnegative potential on the grid alc of tube 4l by allowing a. negativecharge to collect on the grid condenser indicated at Li7 through theresistance 40 and connection to ground which is normally maintained atnegative potential with respect to the cathode 41a through resistance 48as previously explained relative to tube 27. The placing of the negativecharge on grid 41e of tube 41 results in reducing the plate current inthe output circuit leading from the anode 41h through relay winding 23in the output circuit which is completed through resistance 33 to thepath of positive plate potential through conductor 34. If the armaturetongue 37 is held in contact with contact 39 a given period depending onthe values of resistance 40 and capacitance 47 and also upon thecharacteristics andoperating constants of the tube employed, thenegative biasing potential will increase until the plate current isreduced to a low value which de-energizes the relay 23. The relaycontacts 22 are thereby closed completing the circuit through the voicecoil 21 of the electrodynamic loud speaker 2G. The system is now in acondition for the reception of a program such as vocal or instrumentalmusic.

When amature tongue 37 is in contact with contact 38, a given perioddepending on the values of resistance l5 and capacitance i7 and thecharacteristics and Operating constants of the tube employed, the chargewill be reduced by leakage through resistance Ii5 until the potential ongrid lllc is of such an order as to allow sin'llcient current to flow inthe output circuit to energize relay .3 and thereby open the circuit tothe voice coil oi the loud speaker rendering it inoperative.

The control circuit of my invention makes use of the fact that thespeaking voice is distinguished from vocal or instrumental music by thediilerences in rate and duration oi the impulses and pauses in theincoming wave trains. rfuese differences are brought out by operation ofthe rectiler circuit as hereinbefore explained.

The characteristics of the audio frequency signals to which the controltube 27 and the relay 32 will respond are further differentiated byreason of the cut-off afforded by the filter elements 28, 29 and 30. Inother words, the average frequency of speech is lower than the averagefrequency of music. An arbitrary cut-oil value of 512 cycles has beenchosen as a suitable frequency since thisl is the second harmonic of theaverage fundamental frequency of a womans speaking voice. This filtercan easily be made adjustable for local conditions. The results of thisdiscrimination between music and speech is to cause the output currentof tube 27 to be practically constant on the reception of music therebycausing relay 32 to be energized the major portion of the time drawingarmature 37 down and establishing connection with contact 39 therebyplacing a negative charge. on the grid 41e and cutting off the platecurrent in the output circuit of tube 41, deenergizing relay 23 andenabling the voice coil circuit to be closed for the reception of music.However, upon the reception of extended speech, the solenoid winding 32is de-energized to a greater extent allowing amature 37 to contact with38 more than with 39 thereby allowing the charge on capacitance 47 andthe grid 41e to be discharged through resistance 45 and conductor 46 tocathode 41a of tube 41. This allows plate current to ow in the output`circuit of tube 41 energizing relay 23 and thereby disconnecting thevoice coil of the loud speaker. In this way, the receiver automaticallyrespondsto the broadcast program so long as instrumental mimic or vocalselections are being transmitted. 'Ihe receiver automatically does notrespond when speech is prolonged on the broadcast program. The powersupply for all of the electron tubes is obtained yfrom the circuitthrough a transformer system 52 having a plurality of windings 53, 54,55 and 56 leading to the different power supply circuits of the receiverand to the rectifier 25 from which the plate potential, biasingpotential and potential for yexciting the field winding 24 of theelectro-dynamic speaker is obtained.

In the event that it is not desired to interrupt the entertainingproperties of the receiving apparatus, in Fig. 2 where the soundreproducing system is switched to an automaticphonograph or-other formof automatic program recording device, 4which will permit thereproduction o f a desired record intermediate the periods ofentertainment broadcasting on the radio receiving system. Reference toFig. 2 shows the system I employ for switching the audio-frequencyampliner portion of the broadcast receiver to the control portion of arecorder circuit by which recorded programs are reproduced electric y.In this arrangement, an auxiliary unitis coup ed to the output circuitof the radio frequency ampliiier stage 9 and connected to a relaycontrol system which functions to connect the phonograph actuatingcircuit into the input of the detector tube for utilizing the detectortube as part of the audiofrequency ampliiier system for reproduction ofmusic from the phonograph circuit when broadcast music isv not beingreceived. This arrangement includes the radio frequency detectorstageindicated at which is coupled through conductor 6l and couplingcondenser 62 with the output of the radio frequency amplifier stage 9.The other side of the input circuit to the radio frequency detectorstage 60 is completed through the impedance l circuit 63 to ground asshown. The output of the radio frequency detector stage 60 is coupledthrough the coupling circuit 64 with the input circuit of theaudiofrequency rectifier tube 65. A filter circuit is employed betweentheoutput circuit of the radio frequency detector 60 and the inputcircuit of the auxiliary detector tube 65 in a manner similar to thefilter circuit heretofore described in Fig. l. That is, lter elements28, 29 and 30 aro arranged in circuit with the audiofrequency rectifiertube v65 to discriminate between the range of voice frequencies and therange of musicalirequencies to which the .radio frequency detector 60responds.

when relay 23 is energized due'to extended l speech or thediscontinuance of the 'musical program, contacts 66 are closed whichvcloses the I may employ the arrangement shown vtive biasing potential ondetector tube 10 so that it operates on the straight portion of thecharacteristic curve instead of the lower knee of the curve, henceemploying it as a linear amplifier. Terminals indicated at 74 connect tocontacts on'the record release switch on the phonograph orreproducingdevice where a sound program such as the telegraphone is employed, thisfeature is obtained by employing an interlocking time' switch, or amechanical or electrical device or impulse on the recording wire torender the radio receiver responsive at the completion of one-or morerecorded selections, so that when the musical program is continued onthe radio receiver it will not interrupt the playing of the record. iThis, of course, is optional and may be eliminated in which case as soonas the radio musical program is resumed, the phonograph will bedisconnected and the radio circuits restored to normal.

Switch 75 is closed when it is desired to render 1 the speecheliminating system inoperative or in other words, when the apparatus isto per-A form as a normal radio broadcast receiver.

In Fig. 3, I have shown equipment which will automatically selectanother station when the musical program is discontinued on the stationtuned in at the'moment. If, after a given period, no music is received,another station will be 116 selected. '1 If the program of this stationis interrupted too long, still another stationwill be selected or arecorded program may be used similarly to that shown in Fig. 2 andhereinafter described. The wiring of the equipment is similar 120 phone71a to permit a full record to be played before returning the soundreproducing'system to the radio connection. If station selectorequipment 80 operates practically instantaneously contacts 8l may beused to place a biaso on the 185 grid 41a of tube 41 to prevent anotheroperation of relay 78 before the selector has operated and to place therelay system in position to operate again if there is no music on thestation for which the radiotfrequency ampliiler circuits have just beentuned to rsonance. If the selector equipment 80 is of a type thatrequires an appreciable time to operate it is advisable to also connectterminals 82 to contacts which are closed only while the selector device80 is operating. III, after a given time, depending on the constants ofre- -sistance 45 and 'capacitance 47. and the characterselector switch79 reaches contacts 83, in the course of itsv clock-wise movement, relay84 is energized operating contacts 67, 68, 69 and 70 as previouslydescribed to disconnect the radio receiving circuit by shunting couplingcircuit 13 and connectingthe phonograph pick-up 71 or telegraphone 71ato tube 10. Contacts 66 close starting the circuit of the automaticphonograph 71 or telegraphone 71a. Contacts 85 are closed whichcompletes a circuit through terminals 86 to momentary contacts on thephonograph record release switch or other indicating device so that theselector switch'79 will be actuated when the record is completed; Whenthe selector switch contacts makes contact with contacts B7, relay 88 isenergized allowing the selector to return to the rst position 89 and thecircuits to tube 10 are restored' to normal.

Switch 90 is opened if it is desired to remain tuned on the same stationbut to eliminate extended speech. If it is desired to substitutephonograph records for the extended speech, switch 90 is closed tocontact 91 and switch 92 is closed. If it is desired to render thedevice entirely inoperative, switch is closed. Contacts 93 open thecircuit to the loud speaker when it is desired only to eliminateextended speech and not subn stitute any other program. Relays 78 and 38are of the quick acting slow release type in order to insure fulloperation of the selector switch.

A multipoint switch operated by a single control may be used for theswitching operations described above.

-The radio frequency detector tube circuit 60 may be used as a volumecontrol system for changing the voltage on the screen grid of the tubesof the radio frequency stages or the circuit may be used to actuate theautomatic coupling device as set forth in my application Serial No.548,695, illed July 3, 1931, entitled Volume control system.

The system oi.' my invention utilizes another difference in thecharacteristics of music and speech for discriminating between them,namely that the periods of no signal in speech integrated over apredetermined period of time, are more pronounced than similar periodsduring music reception. This is illustrated in Fig. 4. At A is shown atypical Wave trace of speech. It will be noted that there are extendedperiods during which the amplitude is zero or very small. By utilizingthe characteristic' differences of the major frequencies found inspeechand music, that is, 'where the low frequencies predominate to arelatively greater extent in speech than in music, the silent period canbe increased to a still greater extent in speech than in music. The wavetrace A shows considerable pause between syllables. The pause betweenwords is usually more pronounced.

Wave trace B shows the same speech traces rectified by the tube 27 of mycircuit (the alternating component and the average plate cur1 rent oftube 27). By properly designing and adjusting relays 32 and 23 thecondenser 51, the

charge'and discharge resistors 40 and 45, respectively, contacts 38,will remain closed for a greater part of the time than contacts 39 (thismay be only relatively speaking depending on the ratio of the timeconstants of the charge and discharge circuits) thereby allowing thenegative charge on the condenser 51 and hence the negative bias on grid41o to be reduced to such an extent as to allow a current or suillcientvalue to operate relay 23 to flow which would render the loud speakingor other reproducing device inoperative by opening the circuit to thevoice coil 21 at contacts 22.

Wave trace C shows the same traces for an average musical selection. Inthis case, although the peaks in the speech may, in certain instances behigher than those in music, the average amplitude of the musicintegrated over a predetermined period of time is higher and moreconstant with very few extended periods of no signal. For this reason,during musical selections or when musical selections are commenced aftera period of silence or extended speech, relay 32 will be loperated agreater portion of the time than during speech (this may he onlyrelatively speaking 'depending on the time constants of the charge anddischarge circuits) which will allow a negative charge to accumulate onthe condenser 51 and grid 41o, thus controlling the plate circuit oftube41 to such an extent as to render re lay 23 inoperative and the loudspeaker or other reproducing device operative by closing the con'l tacts22 and completing the circuit through voice coil 21.

While I have described my invention in certain preferred embodiments, Idesire that it be understood that modifications may be made and that nolimitations are intended other than are imposed by the scope of theappended claims.

What I claim and desire to secure by Letters Patent of the United Statesis as follows:

1. In a radio receiving system, means for receiving signaling energy, asound reproducing system, an auxiliary control circuit connected withsaid signal receiving means and means controlled by said auxiliarycontrol circuit for discriminating against programs of differentcharacteristics received by said signal receiving means forcorrespondingly controlling the continuity of the circuit between saidsignal receiving means and said sound reproducing system.

2. In a signal receiving system, means -for receiving signaling energy,a sound reproducing circuit, an auxiliary control circuit connected withsaid signal receiving means, a relay device operated by said auxiliarycontrol circuit, said re lay device operating according to the characterof the program received by said signal receiving means for controllingthe continuity of the circuit between said sound reproducing System andsaid signal receiving means.

3. In a signal receiving system, a circuit for receiving signalingenergy, a sound reproducing system connected with said circuit, anauxiliary control circuit connected with said receiving circuit, a relayoperated by said auxiliary control circuit, said relay operating to openor close the circuit through said soun'cl reproducing system withrespect to said receiving circuits according to the character of thereceived signaling energy.

4. In a signal receiving system, a circuit for receiving signalingenergy, a sound reproducing circuit, an auxiliary control circuitconnected `with first mentioned circuit, a relay operated by saidauxiliary control circuit and means controlled by said relay forelectrically connecting or disconnecting said sound reproducing circuitwith respect to said signal receiving circuit acccrding to the characterof the received signaling .energy 5. In a radio broadcast receivingsystem, a sign nal receiving circuit responsive to speech or musicalprograms, a sound reproducing system, an auxiliary control circuitconnected with said i'lrst mentioned circuit, a relay operated by saidauxilnasales iary control circuit, means connected with said auxiliarycontrol circuit for discriminating between average frequencies of speechprograms and average frequencies of musical'prcgrams, said I relayoperating to control the electrical connection of said sound reproducingcircuit with said signal receiving circuit in accordance with thecharacter of the received program.

6. In a radio receiving system, means for receivlng signaling energy, asound reproducing system, an auxiliary control circuit connected withsaid signal receiving means and means controlled by said auxiliarycontrol circuit for dis` criminating between speech programs and musilcal programs received by said signal receiving means for controlling theelectrical circuit between said signal receiving means and said soundreproducing system and rendering said sound reproducing systeminoperative with respect to go said signaling energy during thereception of the speech programs and operative during the reception ofmusical programs.

7. In a signal receiving system. means for-receiving signaling energy,asound reproducing circuit, an auxiliary control circuit connected withsaid signal receiving 'ineans, a relay device operated by said auxiliarycontrol circuit, and an electron tube circuit controlled by said relaydevice, said electron tube circuit being variably biased according tothe character of the program received by said signal receiving means forcontrolling the continuity of the circuit between said sound reproducingsystem and said signal receiving means for correspondingly controllingthe operation of said sound reproducing system. 8. In a signal receivingsystem, a circuit for receiving signaling energy, a sound reproducingsystem connected with said circuit, an auxiliary control circuitconnected with said receiving circuit, a relayfoperated by saidauxiliary control circuit, an electron tube circuit connected with saidrelay and controllable according to the bias potential impressed thereonandv switching means controlled by said relay and operating to openorclose the electrical circuit through said sound reproducing systemaccording to the' character ofthe received signalingenergy forcorrespondingly controlling the operation of said sound reproducingsystem.

9. In a signal receiving system, a circuit for receiving signalingenergy, a sound reproducingcircuit, an auxiliary control 'circuitconnected with said first mentioned circuit, a relay operated by saidauxiliary control circuit, an electron tube'circuit having an inputsystem and an output system, means controlled by said relay forcontrolling. the character of the bias potential in said inputsystemnepending upon the character of the received4 signaling energy andcorrespondingly controlling the operation of said output system and acircuit controller in said output system operating to electricallyconnect or disconnect said sound reproducing circuit with respect vtosaid signal receiving circuit according to the characterv of thereceived signaling energy for correspondingly controlling the operationof said sound reproducing circuit.

10. In a radio broadcast receiving system, a signal receiving circuitresponive'to speech'or musical programs, a soimd reproducing system, anauxiliary control circuit connected with said mst mentioned circuit, anelectron tubeoperated by said auxiliary control circuit, a relayoperated by'said'electrontube. means connected with said T5 auxiliarycircuit for controlling the bias potential impressed upon saidelectron'tube for selectively controlling said relay for discriminatingbetween average frequencies of speech programs and average frequenciesof musical pro-` grams, said relay operating to control the electricalconnection o f said sound reproducing. circuit with respect to saidsignal 'receiving circuit in accordance with the character of thereceived program.

ll. In a signal receiving system, a signal receiving circuit, a controlcircuitconnected with said signal receiving circuit, a relayelectrically operated by said control circuit, means controlled by saidrelay for selectively tuning said signal receiving circuit, and means insaid control circuit for maintaining said relay inone condition uponreceipt of musical productions and in another condtion upon receipt ofvoice programs of predetermined length,

, 12. In a signal receiving system, a signal receiving circuit, a soundreproducing circuit connected therewith, a control circuit operated fromsaid signal receiving circuit, va relay.electrically actuated by saidcontrol circuit, a nlter circuit interposed between said control circuitand said relay for discriminating between average voice frequencies andaverage musical frequencies, said relay being operated under differentconditions upon receipt of extended speech programs as distinguishedfrom musical programs fory correspondingly controlling the 'operation ofsaid sound reproducing circuit with respect to said signalreceivingcircuit.

13. In a signal receiving system having means for discriminating betweenvoice programs and musical programs, a signal receiving circuit, a

sound reproducing circuit connected with said signal receiving circuit.,an electron tube control circuit, a relay electrically operated by saidcontrol circuit, means for biasing said electron tube control circuit toa predetermined cut-oil value for deriving a direct current variationcorresponding to the incoming signalling energy, means disposed in saidelectron tube control circuit responsive to a greater extent to musicalfrequencies than voice frequencies whereby the average current suppliedto said relay is greater upon the reception of musical frequencies thanupon the reception of voice frequencies, the character ofthe musicalfrequencies being substantially 12g continuous as distinguished from theintermittent pauses inherent in the voice frequencies, whereby the relayis energized a greater proportion of the time during thereception ofmusic frequencies than during the reception of voice u@ frequencies forcorrespondingly controlling the connection of said sound reproducingcircuit with said signal -receiving circuit.

14. In a signal receiving system, a signal receiving circuit, a soundreproducing circuit conl nected with said signal receiving circuit, acontrol circuit connected with said signal receiving circuit,-a relayelectrically connected with said soundv reproducing circuit forcontrolling the connections between said sound reproducing ciro cuit andsaid signal receiving circuit, saicll control clrcuit including auelectron tube connect ed with said relay, and means for impressingpredetermined biasing potential uponv said electron tube, said meansoperating to change the biasing potential upon said electron tubeaccording to the character of the incoming program whether a voiceprogram or a musical program for controlling the operation'of said relayand correspondingly controlling the yconnection' of 15 said soundreproducing circuit with said signal receiving circuit.

15. In a signal receiving system, a signal receiving circuit, asoundreproducing circuit, a relay system for controlling the connection ofsaid sound reproducing circuit with said signal receiving circuit, acontrol circuit electrically connected with said signal receivingcircuit, an electron tube including a cathode, a control grid and ananode, said control grid being connected with said signal receivingcircuit, said anode being connected with said relay system, and means:for changing the bias potential on said control grid according to thecharacter of the incoming program for actuating said relay system in oneneeted with said signal receiving circuit. a relay electrically actuatedby said control circuit for nal receiving vcircuit on a signalingchannel carrying a musical program as distinguished from a voiceprogram.

17. In a signal receiving system, a signal receiving circuit responsiveto a multiplicity of different signaling channels over a predeterminedrange of frequencies, a sound reproducing circuit electrically connectedwith said signal receiving circuit, means for automatically tuning saidsignal receiving circuit to a selected signaling channel, a relay systemfor controlling the operation of said automatic means, and a controlcircuit operative according to the character of the incoming program foractuating said relay system for selectively tuning said signal receivingcircuit to a signaling channel carrying a musical program asdistinguished from signaling channels carrying a speech program forcorrespondingly actuating said sound reproducing circuit.

GEORGE P. ADAIR.

